By Ranger Steve Mueller
Cherries and plums for our Christmas festivities depend on crop production. Michigan has an important cherry orchard industry. We eat cherries throughout the year and I particularly like Traverse City Pie Company cherry pies.
The American Plum Borer is a micro moth that few people ever see but it feeds on cherry and plum trees. It is the most important pest of these trees in Michigan. Natural control species such as birds, spiders, beetles, ants, and wasp parasitoids are important for maintaining pest control.
Legislation has been introduced to revise the definition of “conservation” regarding biological diversity to remove key provisions regarding restoration, distribution and the “continued existence” of native species and communities. It would prevent biodiversity from being considered when managing natural resources. Biodiversity is fundamental to healthy functioning nature niches. It is beyond my comprehension and the scope of the article to address political motivations that undermine maintenance of healthy ecosystems. By the time this article is printed the vote will likely have occurred.
The focus here is on the American Plum Borer, Euzophera semifuneralis (Walker), a Pyralid moth and other species that control it. Like so many aspects of the natural world, very little is known about the moth’s biological control despite it being the most important pest of the cherry and plum trees. A change in how we harvest cherries is one reason it is an important pest. About 40 years ago we shifted to hydraulic tree shakers from human manual pickers. The mechanical harvesting by machines instead of humans causes cracking and tearing of the bark.
The moth lays eggs that hatch and enter through the bark injuries. Caterpillars feed on the thin cambium that produces new tissue for transporting food, water, and nutrients. Trees usually die within five years if the insects are too abundant. To control the insect, pesticides are used but pesticides used are being discovered as harmful to us. They are increasingly restricted to safeguard our health. That makes a case for maintaining natural biodiversity of native species to help control the insect that takes food from our tables.
A variety of birds including the Northern Flicker and other woodpeckers were commonly found probing the bark in spring and summer for moth larvae. White-breasted Nuthatches and other birds search the tree wounds and bark for larvae and over-wintering hibernators.
The most common parasitoid eating the moth larvae is a tiny ichneumon wasp. Parasitoids are different from parasites in that they kill their prey. They feed inside the caterpillar on non-vital tissues at first and later eat vital organs causing death. A true parasite does not kill its host. A mosquito is a good example of a parasite on us.
Crab spiders species were found preying on the moths. A beetle, nematode roundworms, fungi, and ants are important natural controls. Many natural control species await discovery. Often when pesticides are used, the natural control species are more severely reduced than the pest species because they are not as abundant. The pest species is then able to reproduce more rapidly in the absence of natural controls and create increased economic harm.
Two things that would help keep cherries on our tables would be to reduce the mechanical damage to tree bark by tree shaker machines and to maintain natural biodiversity so native species are able to continue their ecological role in the food web. One might think it would have minor impact for politicians to prevent scientists and land managers from using best practices to maintain biodiversity but their action can be devastating. Details about the biological control of the American Plum Borer can be found in a scientific paper written by David Biddinger and Tim Leslie in the Spring/Summer 2014 issue of The Great Lakes Entomologist journal.
Natural history questions or topic suggestions can be directed to Ranger Steve (Mueller) at the firstname.lastname@example.org Ody Brook, 13010 Northland Dr, Cedar Springs, MI 49319-8433. 616-696-1753.